Sodium dichromate - Na<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>

What is Sodium dichromate?

Na2Cr2O7 is an inorganic compound with chemical name Sodium dichromate. It is also called Bichromate of soda or Disodium dichromate or Sodium dichromate (VI). It is a powerful oxidizing agent and highly corrosive.

Bichromate of soda is a red to red-orange crystalline solid. It is odourless and dissolves in water, methanol as well as ethanol. It is widely used as a corrosion inhibitor. On heating it liberates toxic chromium fumes.

Properties of Sodium dichromate – Na2Cr2O7

Na2Cr2O7

Sodium dichromate

Molecular weight of Na2Cr2O7

261.97 g/mol (anhydrous)

Density of Sodium dichromate

2.52 g/dm3

Melting point of Sodium dichromate

356.7 °C

Boiling point of Sodium dichromate

400 °C

Sodium dichromate structure – Na2Cr2O7

Structure of Sodium dichromate

Na2Cr2O7 Uses (Sodium dichromate)

  • Sodium dichromate is a primary material in the manufacturing of chromium chemicals.
  • Used as textile dyes.
  • Used in water treatment.
  • Used in leather tanning.
  • Used as a catalyst.
  • Used as an oxidising agent in the manufacturing of synthetic organic chemicals.
  • Used in the refining of petroleum.
  • Used in metal treatments such as electro-engraving of copper.
  • Used in Colorimetry experiment to determine the amount to copper.
  • Used as an insecticide and fungicide.
  • Used as a colourant in glass.

Production of Sodium dichromate

On a large scale, Disodium dichromate is obtained from ores that contain chromium(III) oxides.

Step 1: Fusing the ore with a base such as sodium carbonate

Step 2: Maintain a temperature at around 1000 °C

Step 3: Conduct the above two steps in the presence of air which is the source of oxygen. The reaction is as follows:

2Cr2O3 + 4Na2CO3 + 3O2 → 4Na2CrO4 + 4CO2

The above steps solubilize the chromium and allows its extraction in the hot water. The other components present in the ore are poorly soluble hence acidification of the resulting aqueous extract with the help of carbon dioxide or sulfuric acid produces dichromate.

2Na2CrO4 + 4CO2 + H2O → Na2CrO7 + 2NaHCO3

2Na2CrO4 + H2SO4 → Na2CrO7 + Na2SO4 + H2O

With the process of crystallization the dichromate is extracted as dihydrate.

Health hazards

Inhalation of dust or mist of Sodium dichromate (VI) causes respiratory irritation which resembles asthma and nasal septal perforation may occur. Swallowing causes diarrhea, and vomiting. When exposed to eyes and skin it results in local irritation and dermatitis.

It is a non-combustible compound but increase combustion of other compounds. It can explode and catch fire when comes in contact with combustible substances.

Learn more about the Structure, physical and chemical properties of Na2Cr2O7 from the experts at BYJU’S.

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